filters: it helps to actually commit the new file

scripts/filters.lua

@@ -0,0 +1,69 @@
+--[[
+Item and inventory filters.
+
+Right now this file just contains a shim to get filters off stuff as a string so
+that we can shove in calls for the 1.1-ish parts of the API to get things off
+the ground, and some other utilities to hack things into working.  This is worth
+a module because it will later need to deal with quality, and also localisation
+of filters.
+]]
+local TH = require("scripts.table-helpers")
+
+local mod = {}
+
+---@alias fa.Filters.Filterlike LuaEntity | LuaInventory
+
+---@param filterable fa.Filters.Filterlike
+---@param index number
+---@return string?
+function mod.get_filter_prototype(filterable, index)
+   print(serpent.line(filterable))
+   local filter = filterable.get_filter(index)
+   if filter then
+      return filter.name --[[@as string]]
+   end
+   return nil
+end
+
+-- cannot be used on inventories, because in inventories the filter indices are
+-- inventory slot indices, not a list of filters.
+---@param ent LuaEntity
+---@return  string[]
+function mod.get_all_filters(ent)
+   local ret = {}
+
+   for i = 1, ent.filter_slot_count do
+      TH.insert_if_notnill(ret, mod.get_filter_prototype(ent, i))
+   end
+
+   return ret
+end
+
+---@param filterable fa.Filters.Filterlike
+---@param index number
+---@param filter ItemFilter?
+function mod.set_filter(filterable, index, filter)
+   filterable.set_filter(index, filter)
+   if filterable.object_name ~= "LuaEntity" then return end
+
+   -- For entities we have to work out when to set use_filters.
+
+   -- Easy case: it is using a filter because this just set one.
+   if filter then
+      filterable.use_filters = true
+      return
+   end
+
+   -- Otherwise check all of them; if we find one turn it on; if we don't turn
+   -- it off.
+   for i = 1, filterable.filter_slot_count do
+      if filterable.get_filter(i) then
+         filterable.use_filters = true
+         return
+      end
+   end
+
+   filterable.use_filters = false
+end
+
+return mod